As exemplarily shown in FIG. 1, an engine-driven supercharger for supercharging an engine comprises a rotor casing 1 having therein male and female rotors 2 and 3 arranged in juxtaposed and meshed relationship. The rotors 2 and 3 have shafts 6 and 7 rotatably supported by bearings 4a and 5a at a front and bearings 4b and 5b at a rear, respectively. One end of each of the shafts 6 and 7 of the rotors 2 and 3 extends through the rotor casing 1 into a gear casing 8 at the front of the rotor casing 1. Timing gears 9 and 10 are mounted on the extensions of the shafts 6 and 7, respectively, in mesh with each other. The gear casing 8 has speed increasing gears 11 and 12 therein in meshed relationship. The smaller-diameter gear 11 is mounted on the shaft 6 of the male rotor 2 while the larger-diameter gear 12 is mounted on one end of an input shaft 14 which is supported by bearings 13a and 13b and extends at its other end away from the rotor through the gear casing 8. A pulley 16 is rotatably mounted through a bearing 17 on an outer periphery of the end of the input shaft 14 extending through the gear casing 8. The pulley 16 is connected through a belt 18 to a pulley 22 mounted on an output shaft of an engine 15 such that output from the engine 15 is transmitted through the pulley 22 and the belt 18 to the pulley 16. Furthermore, an electromagnetic clutch 19 is arranged between the pulley 16 and the input shaft 14 such that rotation of the pulley 16 is transmitted to the rotors 2 and 3. When the electromagnetic clutch 19 is on and the rotating power of the engine 15 is transmitted through the pulley 22 and the belt 18 to the pulley 16, the rotation of the pulley 16 is transmitted through the electromagnetic clutch 19 to the input shaft 14, is accelerated through the speed increasing gears 12 and 11 and then is transmitted to the timing gears 9 and 10. The male and female rotors 2 and 3 are timed in rotation in the rotor casing 1 by the liming gears 9 and 10 so that air sucked through a suction port 20 at the rear of the rotor casing 1 is compressed, is delivered through a delivery port 21 at the front of the rotor casing 1 and is supercharged to the engine 15. Reference numerals 23a and 23b denote sealing means.
In the the engine-driven supercharger described above, because of the rotors 2 and 3 being rotated at high speed, the bearings 13a and 13b for supporting the input shaft 14, the bearings 4a, 5a, 4b and 5b at the front and rear for supporting the shafts 6 and 7 of the rotors 2 and 3 and the like must be prevented from being worn out. For this purpose, so far an internal enclosing system has been employed in which a lubricating oil is enclosed in the front and rear of the rotor casing 1 so that oil films are formed by the enclosed lubricating oil over sliding surfaces of the respective bearings.
High speed rotation of the rotors, however, causes an amount of heat generated to be increased, which raises in temperature the delivered air and consequently the casings 1 and 8 so that the lubricating oil is increased in temperature by such generation of heat. As a result, in the above-mentioned internal enclosed lubrication, there are fears that no oil film may be formed over the sliding surfaces and that once raised in temperature, the lubricating oil is hard to forcedly cool. These will accelerate contact of the metal sliding surfaces of the bearings with each other, resulting in the sliding surfaces being readily worn out.
To overcome these problems, a so-called external oil feed system has been proposed in which the lubricating oil is fed from an exterior to the rotor casing 1 and gear casing 8, is passed through parts to be lubricated at the front and rear of the rotors and is discharged out of the rotor casing 1 (Japanese utility model 2nd publication No. 3-8690).
The supposed external oil feed type engine-driven supercharger is structurally similar to the supercharger shown in FIG. 1 in that the air sucked through the suction port 20 at the rear of the rotor casing 1 is compressed, is delivered through the delivery port 21 at the front of the rotor casing 1 and is supercharged to the engine 15 and comprises, as schematically shown in FIG. 2, an oil feed port 24 at the front of the rotor casing 1 for introducing part of an engine oil to feed the same as lubricating oil and first and second oil discharge ports 25a and 25b respectively at the front and rear of the rotor casing 1, the lubricating oil 0 from the feed port 24 being passed through a lubricating oil passage 26 between the rotors 2 and 3 in the rotor casing 1 to the bearings 4a, 5a, 4b and 5b to be lubricated at the front and rear and being discharged through the first and second discharge ports 25a and 25b.